1 cup heavy cream
5 tablespoons unsalted butter, cut into pieces
½ tsp vanilla
1 vanilla bean, split and scraped
1¼ teaspoon fleur de sel (or sea salt), plus more for sprinkling
1½ cups granulated sugar
¼ cup light corn syrup
¼ cup water
1. Line bottom and sides of an 8-inch square baking pan with parchment paper, then lightly butter parchment.
2. Bring cream, butter, vanilla, vanilla beans, the vanilla pod, and sea salt to a boil in a small saucepan, then remove from heat and set aside.
3. Boil the sugar, corn syrup, and water in a 3- to 4-quart heavy saucepan over medium heat, stirring until sugar is dissolved. Boil, without stirring but gently swirling pan, until mixture is a light golden caramel.
4. Remove the vanilla pod and carefully stir cream mixture into the caramel (mixture will bubble up) and simmer, stirring frequently, until caramel registers 248 on thermometer. Pour immediately into the prepared baking pan and cool 30 minutes. Sprinkle another pinch or two of salt over the top of the caramel and let sit until completely cooled. Cut into 1-inch pieces (a pizza cutter is perfect for this), and then wrap each piece in a 4-inch square of wax paper, twisting 2 ends to close.